OBD-I Codes List

Ford 79 A/C or defrost on during self test

Make
Ford (1981-1995)
Category
Body
Severity
Check Engine Light

How to read it

Code 79 reads as 7 flashes, pause, 9 flashes on the check-engine light. Jumper the self-test input to signal return at the test connector, then run the key on engine off self test and the running self test, counting the check-engine flashes each time.

New to flash codes? The How to Read Ford EEC-IV Self-Test Codes walks through the test and what the numbers mean. The general OBD-I guide covers the rest.

What does Ford code 79 mean?

A/C or defrost on during self test

Common causes of 79

  • The A/C or defrost was left on during the self test.
  • The A/C switch is stuck closed.
  • The wiring from the A/C switch is damaged or shorted.
  • The ECM sees the A/C input on when it should be off.

How to fix 79

  1. Turn the A/C and defrost off and run the self test again.
  2. Check the A/C switch and confirm it opens when off.
  3. Check the wiring from the A/C switch to the ECM for damage or a short.
  4. Test the A/C switch and replace it only if it fails its own test.
  5. Test the ECM last, only after every circuit test has passed.
  6. Clear the code, then retest to confirm the A/C input reads off during the self test.

Source

Source review recorded

Sources and review

Review: checked against the recorded source material.

  • EEC-IV Ford trouble code table (MIL, description, type)

    archived reference page (troublecodes.net via Wayback Machine)

    Supports: code identity and meaning

    Fetched directly. Code row matches the description used in the data file.

    https://web.archive.org/web/20030720231430id_/http://www.troublecodes.net:80/Ford/eec-iv.shtml

  • Ford EEC-IV trouble codes, Crown Victoria, Mustang, Taurus, Thunderbird 1992-1995 (code, fault location, probable cause)

    archived reference page (troublecodes.net via Wayback Machine)

    Supports: code identity and probable causes

    Independent table on the same archive site with matching code identity and additional probable causes.

    https://web.archive.org/web/20160502051413id_/http://www.troublecodes.net:80/ford/crown-victoria-mustang-cobralxgt-taurus-thunderbird-1992-1995/

  • Ford EEC-IV trouble code table: code, fault location, probable cause (Crown Victoria, Mustang, Taurus, Thunderbird 1992-1995)

    reference page (troublecodes.net)

    Supports: per-code probable causes used for the page cause list and test order

    Fetched 2026-09-30. The probable cause column is what the page lists, in source order, with the test order built from it.

    https://www.troublecodes.net/ford/crown-victoria-mustang-cobralxgt-taurus-thunderbird-1992-1995/

Last updated 2026-10-10.

Report a correction for 79. Include your vehicle, the issue and a source if you have one.

Related Body Codes